When Pope Paul VI released his famous encyclical outlawing artificial birth control, Humanae Vitae,
most evangelicals responded with disregard — perhaps thankful that
evangelicals had no pope who could hand down a similar edict.
Evangelical couples became devoted users of birth control technologies
ranging from the Pill to barrier methods and Intrauterine Devices
[IUDs]. That is all changing, and a new generation of evangelical
couples is asking new questions.
A growing number of evangelicals are rethinking the issue of birth
control–and facing the hard questions posed by reproductive
technologies. Several developments contributed to this reconsideration,
but the most important of these is the abortion revolution. The early
evangelical response to legalized abortion was woefully inadequate. Some
of the largest evangelical denominations at first accepted at least
some version of abortion on demand.
The evangelical conscience was awakened in the late 1970s, when the
murderous reality of abortion could not be denied. A massive realignment
of evangelical conviction was evident by the 1980 presidential
election, when abortion functioned as the fuse for a political
explosion. Conservative Protestants emerged as major players in the
pro-life movement, standing side-by-side with Catholics in the defense
of the unborn.
The reality of abortion forced a reconsideration of other issues in turn.

That's in accord with Benedict XVI's long-held view that the true common ground to be found among serious Christians with serious doctrinal disputes is in work in common for socio-political goals such as the defense of life and defense of marriage.

Among three reasons he gives for evangelicals to look again is the obvious prophetic nature of Paul VI's encyclical on contraception.

we should look closely at the Catholic moral argument as found in Humanae Vitae.
Evangelicals will find themselves in surprising agreement with much of
the encyclical’s argument. As the Pope warned, widespread use of the
Pill has led to “serious consequences” including marital infidelity and
rampant sexual immorality. In reality, the Pill allowed a near-total
abandonment of Christian sexual morality in the larger culture. Once the
sex act was severed from the likelihood of childbearing, the
traditional structure of sexual morality collapsed.

The part I don't agree with comes at the end where he suggests the natural law is good as far as it goes but Christians must rely on the Bible....as is the Bible ever contradicts natural law or vice versa. Truth is Truth or it's not the truth. And then he caricatures Church teaching to say something it emphatically doesn't say (you must bear as many children as you can). But I'll take it. You cannot take a question to prayer with a genuinely open heart and not end up at the door St. Peter's.

What's fascinating is that many Catholics are unwilling to read or engage a papal encyclical and many Protestants increasingly are. That's because the papacy is given the Church -- the entire Church-- as a gift, and the pope is the pope of all Christians, even those who don't acknowledge him as such. It's also an indication as Isaiah says, that God's word does not return to him void. It will always find a hearing and a resting place... just not always in the hearts we expect, or the ones with greatest obligation.